package com.kaoshi.myweb.webtest.java.collection;

import java.util.HashMap;
import java.util.HashSet;
import java.util.Hashtable;
import java.util.LinkedList;
import java.util.Map;
import java.util.Set;

public class Collections {
	public static void main(String[] args) {
		Map<String, String> map = new HashMap<String, String>();
		map.put(null, null);
		
		//HashMap允许 key 为 null，HashTable不允许key 为 null，线程安全，重复的key会替换，
		map.put(null, null);
		
		
		System.out.println(map.size());
		for (Map.Entry<String, String> string : map.entrySet()) {
			System.out.println(string.getKey());
		}
		
		Hashtable<String, String> hashtable = new Hashtable<String, String>();
		
		
		LinkedList<String> linkedList = new LinkedList<String>();
		
		Set<String> set = new HashSet<String>();
		set.add("sdf");
	}
}
